The invention pertains to filter assemblies. More particularly, the invention relates to air filter assemblies that may be used in industrial ovens, including for example relatively high temperature ovens.
Some applications for air filters are in the field of industrial ovens. These ovens can be broadly classified as relatively low temperature ovens, that operate up to 250xc2x0 C., and so-called high temperature ovens, which generally operate above 250xc2x0 C. up to 500xc2x0 C.
It is often desirable to operate these ovens in a clean room environment. In such environments, the ovens are often desired to have HEPA (high efficiency particulate air) filters or ULPA (ultra low particulate airxe2x80x94a higher cleanliness level than HEPA) filters. Conventional HEPA or ULPA filters generally have a pleated woven filter media that has a generally accordian structure and is supported by a perimeter steel frame. The pleated filter material is generally bonded at its edges to the steel frame by a silicone material. The silicone serves as a bonding agent to attach the pleated filter media to the steel frame at the edges of the media, and also serves as a sealing agent to prevent leakage at the attachment of the filter media to the frame.
A disadvantage of such filter assemblies using silicone is that in typical applications the silicone can generally only be rated to have sufficient useful surface life up to 250xc2x0 C. Thus, although the pleated filter media and the steel frame could survive temperatures in excess of 500xc2x0 C., these filters are limited to use only up to 250xc2x0 C. due to the limitation imposed by the silicone bonding and sealing structures.
Thus, there is a need in the art for air filters that can operate at greater than 250xc2x0 C. One solution to this problem has been to use a ceramic adhesive instead of the silicone. However, filters using ceramic suffer the disadvantages that the ceramic is brittle and sometimes cracks, and that the ceramic sheds particles, which is not suitable in a clean environment. Another approach has been to design the oven to have a continuous cooling feature where the air inside the oven is cooled before passing through the filter. The air is then reheated back to operating temperature before passing through the product workspace. This solution takes advantage of having a high cleanliness silicone type filter assembly, but requires additional complexity in the oven design in order to accomplish the cooling and reheating of the air, and also leads to further complexity getting desired temperature uniformity in the workspace.
Accordingly, it will be appreciated that there is a need in the art for a filter than can take advantage of the desirable properties of attending filter media to a rigid frame, and that can in some embodiments provide the ability to operate at relatively high temperatures.
The invention provides filter assemblies that overcome the above difficulties at least to some degree, and is capable of providing filters using filter material within a rigid perimeter frame capable in some embodiments of operating at relatively high temperatures.
There has thus been outlined, rather broadly, the more important features of the invention in order that the detailed description thereof that follows may be better understood, and in order that the present contribution to the art may be better appreciated. There are, of course, additional features of the invention that will be described below and which will form the subject matter of the claims appended hereto.
In this respect, before explaining at least one embodiment of the invention in detail, it is to be understood that the invention is not limited in its application to the details of construction and to the arrangements of the components set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments and of being practiced and carried out in various ways. Also, it is to be understood that the phraseology and terminology employed herein, as well as the abstract, are for the purpose of description and should not be regarded as limiting.
As such, those skilled in the art will appreciate that the conception upon which this disclosure is based may readily be utilized as a basis for the designing of other structures, methods and systems for carrying out the several purposes of the present invention. It is important, therefore, that the claims be regarded as including such equivalent constructions insofar as they do not depart from the spirit and scope of the present invention.